Patent GB-986276-A (GB)
Title: Character recognition
IPC: G06V10/75
Filed: 1962-02-26
Abstract: 986,276. Automatic character reading. INTERNATIONAL BUSINESS MACHINES CORPORATION. Feb. 26,1962 [March 3, 1961], No. 7423/62. Heading G4R. In character recognition apparatus scanning means provide a series of signals representing the character, and further means provide from this series, signals representing the autocorrelation function of the series, the autocorrelation signals being further modified and used to recognise the character. The character 1, Fig. 1, is scanned in a raster by a cathode ray tube 5, signals from photo-cell 7 being applied to an autocorrelation function generation 9. This consists of a 22-stage shift register the photo-cell signals being gated into the register by 45 shift pulses, one for each of the 5 x 9 cells of the character area. For each stage of the register there is a gate connected to the input, so that as the character signals step through the register each gate produces a number of pulses representing the number of overlaps the original character pattern 1 would make with itself in various relative positions, a gate corresponding with each displacement position. The pulses are passed to a second-difference operator circuit 11 in which the table of numbers Fig. 11 representing the autocorrelation function is multiplied by a second-difference operator to increase the black/white discrimination. Each gate lead is connected to an amplifier giving positive and negative outputs. These outputs pass to integrators which sum the sequence of pulses. The second-difference operator is applied by passing the positive amplifier outputs to the corresponding integrators through resistors valued "1" and the negative amplifier outputs to integrators corresponding to the four neighbouring cells (above,below and on each side) through resistors weighted 4. By this means the positive signal in the central position is four times the negative signals in the other four positions. The integrators sum the succession of signals and their final outputs give the seconddifference junction Fig. 11. Each output is applied to a threshold circuit 13 giving a three-state signal depending upon whether the signal was greater, equal to or less than zero to produce the final table as shown in Fig. 12a. Amplifiers produce positive and negative versions of the input which are connected through equal resistances to ten output leads. Each lead is connected to the positive outputs of those amplifiers which correspond to positions having "1" in the table,and the negative outputs of those amplifiers corresponding to "-1". No connection is made to the amplifiers corresponding to positions having zeros in the table. Each character lead receives a signal which depends upon the match between its non-linearly weighted second-difference function and the corresponding signals produced from the scanned character. Because the characters are of different areas,the maximum signals, i.e. the signals generated in the corresponding leads by the ten characters, are different. They must therefore be normalised before being applied to the highest signal detector. This is done by connecting each character lead to earth through a suitably weighted resistor. A transistor circuit 17 finds the lead having the highest signal, the transistor connected to the highest lead conducts and prevents conduction of those connected to any other leads. If two transistors should conduct a reject circuit responds to reject the character. One of ten lamps may light to indicate the character identified. In practice many more cells than 45 are necessary and the circuitry is correspondingly multiplied. The circuit is described in detail with reference to Fig. 22 (not shown).